Vehicle suspension system

ABSTRACT

A vehicle suspension system that resiliently supports a suspended portion of a vehicle on a non-suspended portion while at the same time preventing pitch and roll that are caused by acceleration, deceleration and turning. The system includes a linear actuator such as a single-acting hydraulic cylinder interconnected through a control system with variable displacement pumps/motors and an accumulator. The accumulator is charged to apply enough pressure in the hydraulic system to support the suspended portion of the vehicle in static condition. The variable displacement pumps along with the controls sense the pressure changes occurring in the linear actuators to prevent movement thereby maintaining a normal, level position of the vehicle.

FIELD OF THE INVENTION

This invention relates generally to suspension systems for vibration andacceleration isolation between members such as for vehicles betweenwheels and the chassis. More particularly, but not by way of limitation,this invention relates to a resilient, damped suspension system forvehicles.

BACKGROUND OF THE INVENTION

Since the advent of vehicles, attempts have been made to provide asuspension system for occupants and cargo carried by the vehicle thatisolate the loads from the rough roads over which the vehicle travels.Also, and more recently with the advent of high speed vehicles, it isdesirable to provide a suspension system which permits the vehicle tocorner at relatively high rates while maintaining the vehicle in aessentially level position. It is also desirable during eitheracceleration or stopping to maintain the vehicle in an essentially levelposition. In terms of art, it is highly desirable to be able to control,if not avoid entirely, the roll and pitch that occurs as the vehiclemaneuvers.

It is not only desirable to provide an active suspension system thatfunctions to negate movements of the vehicle away from the level, but toprovide a relatively comfortable system of suspension including dampingof vibrations or movements between the suspended and non-suspendedportions of the vehicle while providing a soft resilient ride for thepassengers and cargo of the vehicle.

Lotus Motor Company has developed for their motorcars an active springrate control which utilizes a hydraulic system with electrohydraulicservocontrol valves and hydraulic linear actuators that are controlledby a computer system responding to an accelerometer and gyrosensormounted on the vehicle. Such system is necessarily complex and extremelyexpensive.

The object of this invention is to provide a practical means ofproviding an active suspension system that is less complex and expensivethan other systems and one that provides an enhanced ride as compared tothe damper controlled systems that are currently in production onvehicles.

SUMMARY OF THE INVENTION

This invention provides an improved suspension system for vehicles thatincludes hydraulic strut means located between the suspended andunsuspended portions of the vehicle, pump and motor means for providingand receiving pressurized hydraulic fluid to and from the strut means,an accumulator means connected to each strut means for supporting theweight of the suspended vehicle members in a static condition, and anaccumulator means connected with the pump means for providingpressurized fluid to the pump and motor means.

Another aspect of the invention contemplates an improved accumulator foruse with the vehicle suspension system that includes a hollow housingand a bellows dividing the housing into first and second compartmentsfor receiving a compressible gas and hydraulic fluid, respectively. Themetal bellows providing a long lasting divider or separator that isdependable and requires no maintenance.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of a vehicle suspension system that isconstructed in accordance with the invention.

FIG. 2 is an enlarged schematic view of a portion of the system of FIG.1.

FIG. 3 is an enlarged view illustrating an accumulator that is alsoconstructed in accordance with the invention.

FIG. 4a, 4b and 4c, are views of variable displacement pump and motorcombinations that are utilized in the suspension system of FIG. 1.

FIG. 5 is a graph illustrating the effect of using the suspension systemconstructed in accordance with the invention.

FIG. 6 is a graph illustrating energy utilization in the suspensionsystem of FIG. 1.

FIG. 7 is a graph similar to FIG. 6, but illustrating a suspensionsystem that does not include the accumulator reservoir of the system ofFIG. 1.

FIG. 8 is an enlarged schematic view of a portion of another embodimentof suspension system that is also constructed in accordance with theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawing and to FIG. 1 in particular, shown therein andgenerally designated by the reference character 10 is a vehiclesuspension system. The suspension system 10 can be utilized in any typeof vehicle, for instance in motorcycles, tanks, and in an automobile tosupport a chassis 12 on wheels 14. The chassis 12 and only two wheels 14are illustrated in FIG.1. The suspension strut assembly 16 is positionedin supporting arrangement between the chassis 12 and the wheel 14.

As shown in FIG. 1, there are four suspension strut assemblies 16, 18,20 and 22. Although only two wheels 14 are illustrated, it will beunderstood that the strut assemblies 20 and 22 also are positionedbetween other wheels (not shown) of the vehicle and the chassis 12.

The strut assemblies 16, 18, 20 and 22 are interconnected by appropriatehydraulic circuits, which will be described, to a pump/motor assemblythat is generally designated by the reference character 24. Thepump/motor assembly 24 is in turn connected to an accumulator assembly26 that also functions as a reservoir for the hydraulic system.Interposed between the strut assemblies 16, 18, 20 and 22 and thepump/motor assembly 24 are control assemblies 28, 30, 32, and 34,respectively. The control assemblies and strut assemblies are similar infunction and only the strut assembly 18 and control assembly 30 will bedescribed more fully in connection with the enlarged, fragmentaryschematic view of FIG. 2.

As shown more clearly therein, the suspension strut assembly 18 includesa hollow body 36 which has a generally cylindrical bore 38 therein.Located in the bore 38 and positioned for reciprocation therein is apiston 40 having a piston rod 42 extending from one end of the body 36.The strut assembly may be described as a single acting linear actuator.

The strut is designed with both ends of the linear actuatorinterconnected. Compression of the strut results in a net fluiddisplacement equal to the rod area times the compression distance. Thisfluid is displaced into the accumulator which in turn compresses the gasthereby increasing the gas pressure. The increased gas pressure isreflected in increased fluid pressure which acts on both ends of thecylinder. The net result being pressure which acts on the rod area whichsupports the externally applied load. The function of the piston is toprovide controlled fluid flow (no leakage past the piston) for damping.

The control assembly 30, as illustrated in FIG. 2, includes a conduit 44located on one side of the piston 40 and conduit 46 located on theopposite side thereof. The conduits 44 and 46 are in communication withthe bore 38. Connected in parallel relationship to the conduit 44 is acheck valve 48, a variable orifice valve 50 and a relief valve 52.

Similarly, the conduit 46 is connected to a check valve 54, a variableorifice 56, and a pressure relief valve 58 which are also arranged inparallel relationship. The check valves 48 and 54 are arranged to permitfluid flow toward the strut assembly 18 while preventing flow in theopposite direction. The variable orifice valves 50 and 56 are providedto produce a controlled pressure drop across the proportional to thefluid flow rate through them to dampen the movement of the piston 40 inthe bore 38. Relief valves 52 and 58 are arranged to open at a presetpressure in the conduits 44 and 46, respectively.

Conduit 60 connects the valve 48, orifice 50 and relief valve 52 inparallel with the valve 54, orifice 56 and relief valve 58. A branchconduit 62 extends to a small gas over hydraulic accumulator 64 thatincludes a compressible gas filled chamber 66 and a hydraulic fluidchamber 68 therein. The accumulator 64 provides resiliency to the strutassembly 18. For example, if the accumulator 64 with the compressiblegas therein were not provided, and the body 36 filed with fluid, thepiston 40 would be rigidly positioned in the cylinder and could not moveunless fluid on one side or the other thereof were displaced. Since thefluid is essentially incompressible, an arrangement of this type wouldprovide virtually rigid connection between the chassis 12 and the wheels14.

However, because of the compressible gas in the accumulator 64,hydraulic fluid on the appropriate side of the piston 40 can bedisplaced into the accumulator 64 compressing the gas contained thereinand permitting movement of the piston 44 and causing the restoration ofthe piston 40 to its initial position.

Only one of the control assemblies which are connected with thesuspension strut assemblies has been described in detail. However, itwill be understood that all of the assemblies may be identical.

Extending from the conduit 60 is a hydraulic conduit 78 that connectsthe control system 30 with a variable displacement pump/motor 80 whichforms part of the pump/motor assembly 24. Similarly, the controlassembly 28 is connected by a conduit 74 which connects the strutassembly 16 with a variable displacement pump/motor 76 that also forms apart of the -pump/motor assembly 24. Conduit 70 extends from the strutassembly 20 to a variable displacement pump/motor 72 and conduit 81extends from the strut assembly 22 to a variable displacement pump/motor82. The variable displacement pumps/motors 72 and 82 also form part ofthe pump assembly 24. As will be more fully described in connection withFIGS. 4a, 4b and 4c, the pumps are preferably vane-type, variabledisplacement pump which upon a reversal flow, may also act as a motor.

As illustrated in FIG. 1, all of the pumps 72, 76, 80 and 82 are drivenby a common shaft 84. The advantage of the single shaft drive is that asingle power takeoff from the vehicle engine can be utilized to drivethe entire suspension system thereby reducing the size, weight and costof the system. An electric motor or other prime mover could be utilizedfor driving the pumps if desired. Further, the pumps 24 could beindividually driven but such an arrangement could overly complicate thesystem and increase its size and cost.

Conduits 86, 88, 90 and 92 connect the pumps 72, 80, 82 and 86,respectively, with the accumulator assembly 26. The accumulator assembly26 is shown in more detail in FIG. 3. This same figure is representativeof the accumulators used with each individual strut. As illustratedtherein, the accumulator assembly 26 includes a hollow housing 94 havinga bellows 96 located therein. The bellows 96 forms a divider in thehousing 94 defining a gas chamber 98 and a liquid chamber 100. The gaschamber 98 is filled with compressible gas such as nitrogen andhydraulic fluid utilized in the suspension system 10 occupies thechamber 100.

The bellows 96 is preferably constructed from metal to insure longevity.Also, it should be pointed out that the volume occupied by the liquidfilling the bellows 96 is somewhat greater than the volume occupied bythe gas since the accumulator assembly 26 also serves as a reservoir forsuch fluid. The relatively large volume of the bellows used for thehydraulic fluid provides for the storage of a considerable amount ofreserve hydraulic fluid that is required to provide adequate resiliencyfor each of the strut assemblies.

The primary function of the accumulator reservoir assembly 26 is toimpose fluid pressure on the entire system 10 so that the pressuredifferential between the reservoir 26 pressure and any steady or staticindividual strut pressure required to support the chassis 12 isminimized. It is intended that the pistons 40 and rods 42 be positionedin the strut assemblies in intermediate positions to permit movement ofthe pistons 40 and rods 42 in either direction.

FIGS. 6 and 7 will describe the reasons for this imposed pressure.

FIGS. 4a, 4b, and 4c illustrates a typical variable displacementpump/motor 72 that may be utilized in the system 10. FIG. 4b illustratesthe position of a the rotor 87 when there is no fluid flow to or fromconduit 70. In this condition, no pumping/motoring action occurs andfluid is simply circulated by vanes 89 when the pump/motor is inoperation. When the suspension system is inactive and the pump/motor isin the no-flow position, a valve may be provided in conduit 70 tocompletely block the strut flow path. In this case, no strut leakdownwill be possible. The valve(s) may be pilot operated, solenoid operated,or operated by some other source indicative of system actuation. Whenfunctioning to provide flow to the conduit 70, the centerline of therotor 87 is displaced as illustrated in FIG. 4a so that fluid is sweptby the vanes 89 from the conduit 86 through the pump 72 and outwardlythrough the conduit 70 toward the strut assembly 20.

FIG. 4c illustrates the condition of the pump/motor 72 when fluid fromstrut 20 passes to the accumulator assembly 26. In this condition, thecenter-line of the rotor 87 has been displaced to the left and fluidflowing from the conduit 70 drives the vanes 89 and the rotor 87 in adirection so that the fluid will return through the conduit 86 to theaccumulator assembly 26.

OPERATION OF THE EMBODIMENT OF FIG. 1

With the vehicle in operation, the pump/motor assembly 24 is also inoperation. Assuming that the vehicle is either sitting still or on avery level road the rotor 89 of the pump 72 is in the general positionshown in FIG. 4b with no fluid being displaced.

If the vehicle is caused to roll about its longitudinal center-line,such as when making a turn or driving along a hillside, the forceapplied to the strut on the low side (outside of the turning vehicle)increases and the force applied to the strut on the uphill sidedecreases. Accordingly, the pressure increases on the downhill side anddecreases on the uphill side. The pressure increases in strut assemblies16 and 22, if the right side of the vehicle is lower and decreases inthe strut assemblies 18 and 20, assuming the left side is higher.

The pumps/motors 76 and 82 have the rotors 87 therein repositioned asillustrated in FIG. 4a upon sensing the compression in the strutassemblies 16 and 22 so that fluid is directed to the downhill strutassemblies 16 and 22. Simultaneously, the extension in the strutassemblies 18 and 20 is sensed and pumps/motors 72 and 80 which have therotors 87 therein are moved to the position illustrated in FIG. 4c sothat fluid flow is toward the accumulator 26. The arrangement is suchthen that upon sensing extension or compression of the struts on oneside of the vehicle as compared to the other, the appropriatepumps/motors 72, 76, 80 and 82 automatically react to provide additionalfluid to the compressed side while receiving fluid from the extendedside, thus restoring the vehicle chassis to the normal level positionwith respect to the wheels 14. Indeed, the system reacts sufficientlyfast so that the vehicle virtually remains in the neutral position.

The forgoing description has been made in conjunction with a vehicleoperating on the side of a hill, but it can be appreciated that suchalso applies to vehicles making a turn since the side of the vehicleaway from the center of the turn is loaded as was the downhill side ofthe vehicle on the hill side. Thus, the reaction of the system 10maintains the vehicle in the normal, level position.

Also, it will be appreciated that all of the components of the system 10are interconnected so that, should pitch occur from either accelerationof the vehicle or sudden deceleration thereof, the appropriatepumps/motors operate to provide additional fluid to the compressed endof the vehicle while receiving fluid from the other end of the vehicle.Thus, the system 10 maintains the normal level position of the vehicleagainst pitching forces.

The aforesaid relationships can be seen in the chart of FIG. 5. Asillustrated therein, the force increase A-C in the struts attempts tomove the piston 40 therein from position C to B. The system 10 operatesto prevent the movement or deflection of the piston 40 and rod 42 from Bto C which would normally occur because the system 10 has almostimmediately provided fluid flow to the loaded strut. The appropriateamount of fluid to accomplish this is automatically provided by thevariable displacement pump/motor assembly 24 described.

The system 10 also provides additional benefits as may be appreciated bycomparing the charts of FIGS. 6 and 7. FIG. 6 illustrates a system, suchas the system 10, wherein the accumulator assembly 26 is not utilized.That is, the system is not preloaded with the static pressure near thestrut pressure required to support the weight of the suspended parts ofthe vehicle. During a turn as illustrated in FIG. 6, the energynecessary to extend the outside inside strut area 99 and the energyrecovered to compress the inside strut area 100 are shown by thecross-sectioned areas under the curve. The total energy required is thedifference of those two areas.

Positioning the rotor 87 of the pump/motor 24 to allow fluid flow fromthe strut 20 to flow to the reservoir allows the recovery of energyindicated by area 100. Recovering this energy minimizes, to the extentpossible, the total energy requirement of the system.

After the turn, energy (area 100) is required to extend the inside strutand energy (area 99) is recovered during compression of the outsidestrut. Thus, the total theoretical energy requirement of the system 10is zero. This is a result of the ability of the pump/motor 24 to allowfluid flow from the strut 20 to flow to the reservoir while thepump/motor is displaced toward the motor position.

In FIG. 7, the same curve is illustrated, but in a system such as thesystem 10 which utilizes the accumulator assembly 26. In this system,the static preload force, that is, the pressure equal to the strutpressure required to support the suspended weight of the vehicle isprovided by the accumulator assembly 26. Accordingly, the energyrequired to extend the outside strut is illustrated by the smalltriangular area 103. The energy required to compress the inside strutshown by the remaining cross-sectioned triangular area 101. The totalenergy required is the sum of the areas 101 and 103. The theoreticalenergy required for the suspension system 10 with or without anaccumulator 26 acting as the reservoir for the pump/motor 24 isidentical. The operating efficiency of the system 10 without theaccumulator 26 will be lower than with the accumulator 26 because theincreased differential pressure across the pump/motor will be higher.All pump/motor devices have lower efficiencies with higher differentialpressures.

In either of the above examples, most of the energy expended isrecovered after the turn or after the imbalance of the vehicle has beenrestored. It should be pointed out that two advantages are provided byintroducing the static preload pressure into the system. Thoseadvantages are: (1) substantially less time is required for the systemto react to the imbalance and be certain that the vehicle remainsessentially at the normal level and position; and (2) that the pumpsoperate more efficiently and will last substantially longer. The longerlife is due to reduction of the pressure differential across the pumps.As can be seen from comparing FIGS. 6 and 7, the pressure does not needto be raised from virtually zero to the maximum required for restorationwhen using the accumulator assembly 26 since the preload pressure isalready in the system 10. At static normal level operation the vehicle,the differential across the pump assembly 24 is nil. The pump assembly24 is operating in an environment wherein the differential pressurethereacross is substantially reduced as compared to a system that doesnot include the accumulator assembly 26.

From the foregoing, it will be appreciated that the preferred embodimentof suspension system 10, an active suspension system that is lesscomplex and expensive than other systems and one that provides anenhanced ride due to the resiliency provided under damped conditions anddue to the ability of the system 10 to maintain the normal levelattitude of the vehicle.

EMBODIMENT OF FIG. 8

FIG. 8 is a partial schematic of a suspension system that is generallydesignated by the reference character 200. In FIG. 8, identical partshave been identified by the same reference characters as used in thedescription of the embodiment 10.

Although not shown, it will be understood that the conduit 70 isconnected to the suspension assembly 20 as was previously described. Theopposite end of the conduit 70, in this instance, is connected to asolenoid controlled multi-port valve 102 which is in turn connected by aconduit 104 with a fixed displacement pump 106. Although notillustrated, a valve 102 and a pump 106 will be provided for each strutassembly 16, 18, 20 and 22.

The valve 102 is connected by a conduit 108 with the accumulatorassembly 26. Accumulator assembly 26 is connected by a conduit 110 withthe inlet to the pump 106.

As illustrated, the valve 102, in addition to pilot operators 112 and114, is provided with a neutral position (N) wherein fluid is deliveredfrom the pump 106 through the conduit 104, through port 105 to a conduit108. The fluid flows through conduit 110 back to the pump 106. As showntherein, in the neutral position (N), the conduit 70 is closed off andno fluid is flowing to the strut assembly 20.

The valve 102 is also provided with a position (C) which is ported insuch a manner that fluid is circulated from the fixed displacement pump106 through the conduit 104 into the conduit 115 and into conduit 108 tothe reservoir accumulator assembly 26 and through the conduit 110returning to the pump 106. A parallel port 116 is connected to theconduit 70 providing hydraulic fluid from the strut assembly 20 to theaccumulator reservoir. When in this position, the strut 20 can compressdue to the bypassing of fluid as previously described.

When it is desired to provide fluid from the pump 106 directly to theconduit 70, the valve 102 is moved to a position (E) which has a port118 that extends directly from the connection with the conduit 104 tothe conduit 70 blocking off the pump flow path to the conduit 108. Whenin this position, fluid flows directly to the strut assembly 20.

While the system 100 operates, it is less desirable than the system 10because it is necessary to constantly reposition the valve 102 toprovide proper flow control to the strut assembly 20 depending on theloading conditions thereof.

Various types of pumps could be utilized in the systems 10 and 100, butthe variable displacement pumps described in connection with theembodiment of FIG. 1 are preferred.

Many changes and modification can be made to the embodiments describedin detail hereinbefore without departing from the spirit o scope of theinvention.

What is claimed:
 1. A suspension system comprising:hydraulic suspensionstrut means for resiliently supporting and damping movement betweensuspended and unsuspended parts of a mass or energy system; flow meansfor providing hydraulic fluid flow to/from said strut means; andaccumulator means for pressurizing said hydraulic fluid, a gas overhydraulic accumulator located at said suspension strut means andconnected with said flow means, said accumulator means including asystem accumulator connected with said flow means to pressurize saidsystem to resiliently support said suspended parts in the staticcondition and to pressurize said flow means to reduce the pressurethereacross.
 2. A suspension system comprising:hydraulic suspensionstrut means for resiliently supporting and damping movement betweensuspended and unsuspended parts of a mass or energy system; flow meansfor providing hydraulic fluid flow to/from said strut means, said flowmeans including a variable displacement pump/motor, said pump/motorpermitting reverse flow therethrough to allow fluid flow from said strutmeans when said strut is to be compressed, permitting no flow, andpermitting forward flow to said strut means when said strut is to beextended; and accumulator means for pressurizing said hydraulic fluid.3. A suspension system for a vehicle that includes a chassis and aplurality of vehicle support ,member, said system including:hydraulicsuspension strut means for resiliently supporting and damping themovement between the chassis and the support members; flow means forproviding hydraulic fluid flow to and from each of said strut means; andaccumulator means for pressurizing said hydraulic fluid, a gas overhydraulic accumulator located at said suspension strut means andconnected with said flow means, said accumulator means including asystem accumulator connected with said flow means to perssurize saidsystem to resiliently support said suspended parts in the staticcondition and to pressurize said flow means to reduce the pressurethereacross when said system is in operation.
 4. The system of claim 3wherein said hydraulic strut means includes:a body member having agenerally cylindrical bore and mounted on one of said parts; a pistonincluding a piston rod located in said bore for reciprocating movementand having said rod connected with the other of said parts; controlmeans connected with said pump means and with said body member forcontrolling the flow of said pressurized hydraulic fluid into and out ofsaid bore on both sides of said piston.
 5. The system of claim 4 whereinsaid control means includes on each side of said piston:a check valvefor permitting fluid flow into said bore and preventing flow in theopposite direction; a variable orifice connected in a parallel flowarrangement with said check valve for damping flow therethrough; and apressure relief valve connected in a parallel flow arrangement with saidcheck valve and variable orifice for permitting flow through said reliefvalve when the pressure in said bore exceeds a predetermined value. 6.The system of claim 5 and also including an accumulator connected withsaid control means, said accumulator including a compressible gaswhereby said piston and rod is resiliently supported by said fluid insaid bore providing resiliency between said parts.
 7. A suspensionsystem for a vehicle that includes a chassis and a plurality of vehiclesupport members, said system including:hydraulic suspension strut meansfor resiliently supporting and damping the movement between the chassisand the support members; flow means for providing hydraulic fluid to andfrom each of said strut means, said flow means including a variabledisplacement pump/motor, said pump/motor permitting reverse flowtherethrough to allow fluid flow from said strut means when said strutis to be compressed, permitting no flow, and permitting forward flow tosaid strut means when said strut is to be extended; and accumulatormeans for pressurizing said hydraulic fluid.
 8. The system of claim 7wherein said pumps/motors have a common drive shaft.